RiceUndeveloped Tapetum1Is a Major Regulator of Early Tapetum Development

Abstract

The tapetum, the innermost of four sporophytic layers in the anther wall, comes in direct contact with the developing male gametophyte and is thought to play a crucial role in the development and maturation of microspores. Here, we report the identification of rice (Oryza sativa) Undeveloped Tapetum1 (Udt1), which is required for the differentiation of secondary parietal cells to mature tapetal cells. T-DNA or retrotransposon Tos17 insertions in the Udt1 gene caused male sterility. The anther walls and meiocytes of the mutants were normal during the early premeiosis stage, but their tapeta failed to differentiate and became vacuolated during the meiotic stage. In addition, meiocytes did not develop to microspores, and middle layer degeneration was inhibited. Consequently, the anther locules contained no pollen. The UDT1:green fluorescent protein fusion protein was localized to the nucleus. This, together with its homology with other basic helix-loop-helix proteins, suggests that UDT1 is a transcription factor. DNA microarray analysis identified 958 downregulated and 267 upregulated genes in the udt1-1 anthers, suggesting that Udt1 plays a major role in maintaining tapetum development, starting in early meiosis.

PERSISTENT TAPETAL CELL1Encodes a PHD-Finger Protein That Is Required for Tapetal Cell Death and Pollen Development in Rice

“…Some genes previously identified as critical for postmeiotic anther development were down-regulated in the ptc1 microarray data (Table I), including a Cys protease (OsCP1; Lee et al, 2004), a fatty acyl-CoA reductase homologous to Arabidopsis MS2 (Aarts et al, 1997), lipid transfer proteins (Osc4, OsC6, YY1, and Os09g0525500; Tsuchiya et al, 1992;Hihara et al, 1996), a stilbene synthase (YY2; Hihara et al, 1996), BURP domain-containing proteins (RA8 and OsRAFTIN; Jeon et al, 1999), a P450 family member (CYP704B2; , a ribosomeinactivating protein (RA39; Jeon et al, 1999), and the putative homolog of AtMYB103 (Higginson et al, 2003;Zhang et al, 2007). Consistent with the RT-qPCR analysis, PTC1 showed up-regulation in the ptc1 mutant (2.97-fold at stage 8, 5.49-fold at stage 9), whereas genes involved in early tapetal and pollen regulation, such as CYP703A3 (Aya et al, 2009), TDR (Li et al, 2006), UDT1 (Jung et al, 2005), and GAMYB (Kaneko et al, 2004;Liu et al, 2010; Table I), showed no significant change. To understand the regulatory role of PTC1, we grouped the 2,417 genes into four COG (for Cluster of Orthologous Groups of proteins) categories: I, information storage and processing (144 genes); II, cellular processes and signaling (363 genes); III, metabolism (551 genes); and IV, poorly characterized genes (1,359 genes; Fig.…”

“…However, transcription factors involved in regulating early tapetal differentiation or sporopollenin synthesis, including GAMYB (Kaneko et al, 2004;Aya et al, 2009;Liu et al, 2010), UDT1 (Jung et al, 2005), TDR (Li et al, 2006), and CYP703A3 (Aya et al, 2009), showed no obvious change ( Table I), suggesting that they act upstream of PTC1 (Fig. 11).…”

“…To aid characterization of the regulatory role of PTC1, the expression profiles of the gamyb-2, udt1, and tdr mutants were compared (Jung et al, 2005;Zhang et al, 2008;Aya et al, 2009). We observed that 40.3% (93 of 231) of the genes changing in tdr, 10.5% (128 of 1,225) in udt1, and 24.2% (210 of 870) in gamyb-2 had expression changes in ptc1 (Supplemental Data Set S3).…”

“…Tapetal cell development and differentiation are critical for the early events in male reproduction, including meiosis; however, during late pollen development, tapetal degeneration, triggered by an apoptosis-like process, is also vital for viable pollen formation (Papini et al, 1999;Varnier et al, 2005;Li et al, 2006;Aya et al, 2009). Currently, although several genes encoding putative transcription factors have been reported to be associated with tapetal function and degeneration, such as Arabidopsis (Arabidopsis thaliana) MYB33/MYB65 (Millar and Gubler, 2005), DYSFUNCTIONAL TAPETUM1 (DYT1; Zhang et al, 2006), ABORTED MICROSPORE (AMS; Sorensen et al, 2003;Xu et al, 2010), and MALE STERILITY1 (MS1; Wilson et al, 2001;Ito and Shinozaki, 2002) and rice (Oryza sativa) GAMYB (Kaneko et al, 2004;Aya et al, 2009;Liu et al, 2010), UNDEVELOPED TAPETUM1 (UDT1; Jung et al, 2005), TAPETUM DE-GENERATION RETARDATION (TDR; Li et al, 2006), and MADS3 (Hu et al, 2011), their detailed functional roles in regulating tapetal PCD during anther development are unclear. We have shown that the Arabidopsis ms1 mutant displays altered tapetal development, with a lack of normal PCD and abnormal tapetal degeneration associated with large autophagic vacuoles and mitochondrial swelling (Vizcay-Barrena and Wilson, 2006).…”

Global Expression Profiling Applied to the Analysis of Arabidopsis Stamen Development

“…Several recent studies have aimed at characterizing gene expression during stamen development on a global scale by microarray analysis (Amagai et al, 2003;Cnudde et al, 2003;Honys and Twell, 2003;Zik and Irish, 2003;Wellmer et al, 2004;Jung et al, 2005;Pina et al, 2005). All of these studies led to the identification of genes with expression in stamens and, in some cases, analyzed specific successive developmental stages (such as during gametophyte development; Honys and Twell, 2004).…”